Fiber optic ribbons include optical waveguides such as optical fibers that transmit optical signals such as voice, video, and/or data information. Fiber optic ribbons generally have a plurality of adjacent optical fibers arranged in a generally planar array in a matrix material. Additionally, the fiber optic ribbons can be arranged as a ribbon stack for a relatively high optical fiber-density.
One optical fiber cable design employing a ribbon stack places the same into a tube filled with a thixotropic material such as grease. Thixotropic materials are used because they are effective at blocking the migration of water inside the tube. Additionally, thixotropic materials function as a friction element inhibiting substantial ribbon stack movement when the fiber optic cable is installed. However, the thixotropic materials are messy and must be removed before the craftsman can optically connect optical waveguides of the optical ribbons. Consequently, “dry tube” designs have removed the thixotropic materials from the tube, but water must still be blocked in the tube. However, conventional dry tubes have disadvantages.
An example of a conventional dry tube design is disclosed in U.S. Pat. No. 4,909,592. This patent discloses a tube having water-swellable tapes and yarns disposed therein for blocking the migration of water. One disadvantage of this design is that voids are formed between the optical fibers, the tube wall, and the water-swellable materials along the length of the tube. Consequently, these voids provide a pathway for the migration of water therealong. Additionally, dry tube designs must maintain sufficient coupling between the optical fibers and the tube wall. Dry tubes accomplish coupling by using the water-swellable materials inside the tube as a frictional element. However, effective coupling requires a substantial amount of water-swellable material that adds expense, thereby increasing cable-manufacturing costs.